1. Field of the Invention
The presently disclosed subject matter relates to semiconductor light-emitting devices, and in particular, to a semiconductor light-emitting device having a configuration in which a semiconductor light-emitting element is mounted on a submount.
2. Description of the Related Art
FIG. 1 shows the configuration of a conventional semiconductor light-emitting device. The conventional semiconductor light-emitting device is configured to include: a submount 51 having a recess 50; a lead frame 52 on which the submount 51 is fixed; a semiconductor laser element 54 placed on the bottom surface 53 of the recess 50; bonding pads 56 connected to a wiring pattern extending from the bottom surface 53 of the recess 50 via an inner peripheral surface 55 (the wiring pattern is not shown in the drawing, but is configured for electrically connecting the electrode of the semiconductor laser element 54 to the bonding pads 56), the bonding pads 56 being provided on the upper face of the side walls of the submount 51; bonding wires 57 for electrically connecting the bonding pads 56 to the lead frame 52; an encapsulating material 58 located in the recess 50 of the submount 51 to seal the semiconductor laser element 54; and a mold resin portion 59 for resin-sealing the submount 51 including the encapsulating material 58, the bonding wires 57, and the lead frame 52. (See, for example, the conventional art reference to Hideo Tamura et al.—Japanese Patent Laid-Open Publication No. 2001-68741.)
In the above-described semiconductor light-emitting device, the submount 51 is fixed on the lead frame 52 via an adhesive. In this instance, the adhesive may spread beyond the outer periphery 60 of the submount 51. For example, when the submount 51 having the recess is fixed on the lead frame 52 by means of an adhesive 70, as shown in FIG. 2, the adhesive 70 is in contact with the outer bottom surface 71 and the outer periphery 60 of the submount 51, and the lead frame 52. At the same time, the adhesive 70 may spread beyond the outer periphery 60 of the submount 51 over the lead frame 52 because it is pressed by the outer bottom surface 71 of the submount 51.
Under this situation, one end of the bonding wire 57 can be connected to the bonding pad 56 provided on the upper face of the side wall of the submount 51, but the other end thereof must be connected to the lead frame 52 at a position which is away from the outer periphery 60 of the submount 51 and is not covered with the adhesive 70 to avoid the adhesive 70 spreading over the lead frame 52.
In this case various problems arise, including the requirement that the bonding wire 57 be long to avoid the adhesive 70. This may increase the material cost, thereby also increasing the overall manufacturing cost. Depending on the amount of adhesive 70 that spreads outward beyond the outer periphery 60 of the submount 51 and the connecting position of the bonding wire 57, the semiconductor light-emitting device may inevitably become large in size. Furthermore, the wiring shape of the bonding wire 57 (loop shape) may change as shown by the dotted circle in FIG. 2 because the wiring length of the bonding wire 57 increases and the bonding wire 57 tends to receive the injection pressure of the mold resin 59 for sealing the bonding wire 57. In this case, the bonding wire 57 may be deformed to weaken the mechanical strength thereof against the resin stress. In other words, the resin stress received by the bonding wires 57 may vary depending on the difference between the thermal expansion coefficients of the bonding wire 57 and the mold resin 59 sealing the bonding wire 57. This may occur due to the high temperature environment during the mounting of the semiconductor light-emitting device on a mother board, or due to the temperature variation environment present due to the repeated turning on/off of the semiconductor light-emitting device mounted on the mother board. As a result of this, the bonding wire 57 may break or come off at its connecting portion or other like problems may occur, causing electrical failure of the connection.
In order to reduce the problems described above, it is conceivable to strengthen the resistance against the injection pressure of the mold resin by adopting a bonding wire with a larger diameter. However, this involves an increase in cost. Alternatively, it is conceivable that the amount of adhesive used for fixing the submount onto the lead frame can be decreased to narrow the range of spreading of the adhesive beyond the submount periphery. In this instance, the bonding wire can be shortened more than the previous case because the range of spreading of the adhesive may be narrowed and the bonding wire can be bonded nearer, in order to strengthen the resistance against the injection pressure of the mold resin. However, this may weaken the bonding strength of the submount to the lead frame.
Another conventional semiconductor light-emitting device is shown in FIG. 3 in which a semiconductor light-emitting element 80 is fixed to the plate-shaped submount 51 via an adhesive 70. In this instance, as in the previous conventional example, the adhesive 70 may spread beyond the side face 72 of the submount 51 outside the bottom surface 82 of the submount 51.
When power is supplied to the semiconductor light-emitting element 80, the light emitted from a side wall 81 side of the element 80 may be absorbed by the adhesive 70 as shown by the dotted small circle in FIG. 3. Therefore, the light utilization efficiency of the semiconductor light-emitting element 80 may deteriorate, thereby making the semiconductor light-emitting device emit light with a lower intensity.